Determination of proliferation index in neoplasms using different Ki-67 equivalent antibodies

Paraffin sections from 23 tumours were immunohistochemically stained with the following four Ki-67 equivalent antibodies: monoclonal MIB-1 (DAKO), monoclonal MM1 (Novocastra), polyclonal NCL-Ki-67p (Novocastra), and polyclonal Rah Ki-67 (DAKO). Ki-67 labelling indices were determined by counting in exactly the same area in each case. MIB-1 showed the highest labelling index in 21 of the 23 cases, and the mean MIB-1 index was approximately 30% higher than that of the other antibodies. The differences between MM1, NCL-Ki-67p and Rah Ki-67 were small and nonsignificant. There was a positive correlation between each of the four antibodies. As these findings may be of importance when the Ki-67 labelling index is used as a criterion for tumour grading or for clinical prognostication, this necessitate identification of the antibody used in every case.